Very simple Audio compressor for FM transmitter

[audioguru]

Many years ago when I worked for Philips soon after they bought Signetics, I used their NE572 dual compander IC (COMpressor or exPANDER). Signetics also invented the NE555 timer IC.

Harris Corp and Alfred and Charles Harris are not and have never been Oriental, they are American. It had strong dealings with GE, RCA and Intersil over its long life.

 

[ronsimpson]

I have a love hate relationship with Behringer. The picture is the left half of a MDX2600. I have a rack full of these and the 4 channel MDX4400.

1) If I am using this ahead of a digital recorder:
I set the Peak Limiter to just turn on at the point where the recorder distorts. It is fast on/off and is also good for peak limiting for broadcast. Also good ahead of the power amplifiers. I have been asked many times why my amplifier/speakers don't distort and how I get so much power out of them.
1a)On the compressor limiter:
If I am truly using it for limiting then the Ratio is set to max. If I am trying to reduce dynamic range to make the music louder then the Ratio is set to 4:1 more or less.
1b)The attack and release time is very adjustable on this unite. I use auto most of the time. In this mode it has two attack and release times. The slow response tries to "ride the volume" over a time period like if a human turned the volume by hand. The fast response tries to catch fractions of a word and is limited to a small range. By running the fast and slow response at the same time you get the benefit of both.
1c)I like to use Interactive Knee which switches into gain reduction mode softly. Over 3bd range. Not as good for peak limiting but sounds better.
1d)The Expander/Gate is good for removing background noise. The Gate can cause bad effects of not used carefully. It just simply turns off the audio if there no volume. The Expander turns down the volume if there is no audio. Sounds better.

2)If I am live and don't know the program well I some times have one of these on every input.
2a)If some one drops a mic or yellows the limiter cuts in and turns down the volume before I could get there.
2b)The Expander might be set to reduce the volume if the mic is not in use.
2c)What I am doing is having the gain adjusted or each channel, just to get it close. Then mix everything together and pass through one last limiter to keep the power amps out of distortion.

3)For "mastering" a recording:
3a)I usually set the levels for the instruments to be as loud as possible with out distortion. Some time each group of instruments are set to this level by them selves. Then I set the vocals to as loud as possible with no instruments. In the Song, the instruments start out full level. When the voices are added in the total is too much. One option is have the limiter turn down the total. (simple) What I usually do is daisy chain the limiters. So then the vocals come in the instruments are reduced. This way the voices stand out over the background. Between the words the background pops back up and gives you the notes to follow.
3b)In some music you want the drums to shake the house but you need the rest of the instruments to be heard. So I set the limiters to "duck" down the instruments and let the drums come through. It sounds like the drums have the power to drive over the rest of the instruments.
3c)This effect works if you have two singers that sing solo and together. The limiter can force the two back to the solo level.
3d)Yes....probably it adds some bad effects. But the voices stand out and your are so custom to hearing this effect in recorded music that it seems normal.

Sorry I talked too much.

 

[MrAl]

Hi,

What is that thing?

I can not find a single reference to show that the CA3080 ic chip is still being made or is going to be made again. If someone has a link please post i'd like to read it over.

We also did not yet talk about DSP. I think the ARM chip i am going to play with can do real time audio processing. The ADC is pretty fast and so is the onboard DAC, although i guess we could use an external parallel ADC and external parallel DAC on several types of microcontroller.
This would be interesting.
I've done real time processing before but this would be the first time for me for anything audio. Would be interesting to see how it turns out. I wonder how the 12 bit DAC would sound. I guess a few tests will be in order. Dont CD players usually use 16 bit? I cant remember now.

 

[ronsimpson]

Dont CD players usually use 16 bit?

yes

 

[Gasboss775]

Gordon:
Where did you get that news from, about the remake of the part? I see their data sheet still is marked "obsolete", and none of the main suppliers seem to stock any although they stock the LM13700. Do you have a link to the article where Intersil states this or something like that?
You got my hopes up that this chip might make a come back

I'm very sorry for getting your hopes up. I could swear that they were being made again by Intersil, perhaps it was a third party, or perhaps a totally different part! I had a stroke a few years ago and my memories not what it used to be. I'll have a look about and see if I can find anything.




If you follow that link you get the "obsolete" marked data sheet.[/QUOTE]

 

[Gasboss775]

Sadly it seems that I was wrong, there is no one manufacturing ca3080 anymore. I have bought and used several sold by Chinese eBay sellers as NOS, don't know if they were genuine NOS or copies, but they all worked. I haven't tested them exhaustively to see if they fit the data sheet specs, but I have built working VCO's, VCF's with them.

Up until the end of last year you could still buy the lm13600N from Tayda Electronics, but I just checked and they only sell the LM13700N now.

I may have been getting confused with the ICL 7660, which Intersil have started making again, I just checked.

Once again sorry for getting your hopes up MrAl

 

[Tony Stewart]

Mr Al no explanation required.

if you read my links Harris parts still avail on EBay

 

[MrAl]

I'm very sorry for getting your hopes up. I could swear that they were being made again by Intersil, perhaps it was a third party, or perhaps a totally different part! I had a stroke a few years ago and my memories not what it used to be. I'll have a look about and see if I can find anything.

Hi again,

No problem, my memory isnt as good as it used to be either
I remembered CA3080E but it was really the CA3080AE.
I might look into the other chip though and see how good that is.

 

[MrAl]

Mr Al no explanation required.

if you read my links Harris parts still avail on EBay

Hi again Tony,

Well it wasnt so much that i wanted buy one right away, i just thought it was nice to hear that they were being made again. It's an old part i guess and things change. They may not have had too many orders for them, relative to what they normally get for most chips. Yeah, some guitar freaks might want them badly to fix their guitar "pedals", but what annual sales volume does that amount to...probably a very low count.

 

[ronsimpson]

but what annual sales volume does that amount to...probably a very low count.

That's the problem with this VCA.

Good news, it was designed by real audio engineers.

 

[MrAl]

That's the problem with this VCA.

Good news, it was designed by real audio engineers.

Hi,

Wow that's a strange one. Single in line package too

I guess we could try to design our own CA3080 or similar using discrete transistors that are commonly available. That might be interesting too.
Probably wont be as stable, but might work anyway.

 

[Gasboss775]

Wow that's a strange one. Single in line package too

That reminds me, there's the ba6110 also 9 pin SIL single ota with a buffer, you can still get NOS on eBay, I just checked.

I have attached the data sheet.

 

[audioguru]

NOS= New Old Stock? I hoarded some old germanium transistors and TTL logic ICs. I wonder if I can sell them on ebay or Kijiji and make a fortune.
When I bought my home it was cheap and out in the boonies but now it is in the middle of a large city that grew around it and is worth a fortune. I wish I bought and hoarded a few more houses when I bought mine.
My car ... never mind.

 

[MrAl]

Hi audioguru,

That reminded me that the germanium transistors were supposed to make a sort of comeback, i read a few years ago (or longer ?). The idea was the germanium and silicon was supposed to be married in some way in order to make fast transistors but lower base emitter drops for driving at lower base voltages. Dont know what happened to that idea as i never heard anything else about it.

I have a couple ancient parts too that are cool to think about. One of the first generation commercial transistors for example.
I used to have some selenium rectifiers removed from old equipment.
Also, (but only) one CA3080

 

[Willen]

*duplicated post deleted!

 

[Willen]

Hi all,
Ok now it's my turn : Here I attached a schematic of a professional audio compressor designed around late 90s. It was a gift for me by Elk Ebert (member here). I want to test the device first before experimenting other simpler limitters. Problem is its inputs and outputs audio connection. It has positive, negative and common (three connections) as input and output. I think it was designed for XLR connections.

From this device I want to record audios (Mic preamp> Compressor> Computer). And I want to compress audios and music for my home made toy FM Transmitter (Mic preamp or MP3 player> Compressor> FM transmitter). Then how to handle or what to add for the 3 audio connections (I think I just need two audio connection)? I don't want to poor solution, but want to simply and better solution. (I still have not got any chance to learn about 3 connection audios like in XLR, I don't know why they use such, curious)!

 

[audioguru]

Willen, you have the input - and Common mixed up/backwards. The common is ground, the - input is not ground.

The compressor has balanced (differential) inputs and outputs. If an input or output does not have a DC voltage (measure them to see) then use the + input and ground as the input and use the + output and ground as the output.
A balanced microphone input on a preamp is commonly used so that any mains hum picked up by the cable gets cancelled. Maybe the compressor has a very sensitive input for a microphone?

 

[ronsimpson]

 

[Willen]

Willen, you have the input - and Common mixed up/backwards. The common is ground, the - input is not ground.

The compressor has balanced (differential) inputs and outputs. If an input or output does not have a DC voltage (measure them to see) then use the + input and ground as the input and use the + output and ground as the output.
A balanced microphone input on a preamp is commonly used so that any mains hum picked up by the cable gets cancelled. Maybe the compressor has a very sensitive input for a microphone?

Hi AG,
I turned ON the compressor 1st time today and measured DC voltage around input and output audio with NO audio injected. Here's a diagram. I wrongly marked input audio polarity in previous same diagram. Here I corrected. You can see DC measurements across Common Vs - and common Vs +.

-Ok then what can I do? (description note has a sentence: "input and output are balanced at line level")
-Another: It operates from +15V to -15V dual supply. My SMPS has not good regulated output. Eg. I get +13.5V and -15V out. What happens if we get such different voltage from dual supply?
------------------------------------------------------------------------------------
Hi Ron,
I just want to connect audio in and out with two wires as I am asking above. The device I got is little different than in the 'Design Notes' of THAT Corp. Thank you for the datasheet and design notre though.

 

[audioguru]

The compressor does not have input or output coupling capacitors so its DC voltages near 0V might mess up your signal source and amplifier.
Now you wrongly show the (+) input connected to ground and the "Common" as a (+) input.

When the wiring is fixed then the (+) input and output can be the live audio signals and the commons are the shielded grounds of their cables.

Your SMPS probably is noisy but its different voltages will not matter.